1. Field of the Invention
The present invention relates to a crucible for use in the melting of metallic materials, and more particularly to a crucible which can be used with a broken arm-type centrifugal casting machine to contain metallic material as it is melted and to then deliver the molten metallic material to an associated casting mold upon the application of inertial and centrifugal forces.
2. The Prior Art
Centrifugal casting machines are well known devices which are used for the casting of small metallic objects. Such casting machines require the use of a crucible which is mounted on the rotatable casting arm of the casting machine so as to be in an operative position with respect to a casting mold, the crucible functioning to support the metallic material (which is to be used in forming the desired object) as it is melted by the flame from a torch and to then discharge the molten metallic material through a channel into the casting mold as the casting arm is rotated. Crucibles for use on centrifugal casting machines have been fabricated in many different shapes--see, for example, U.S. Pat. Nos. 1,778,652; 2,006,148; 2,438,817; 2,847,738; 3,371,705; and 3,648,762.
A currently preferred type of centrifugal casting machine one that is used by many dentists for forming dental prostheses for their patients--is the broken arm-type centrifugal casting machine. In this machine, both the crucible for supporting and housing the metallic material to be cast and the casting mold in which the metallic material is to flow are mounted on a swing arm which is in turn pivotally mounted at one end of a rotatable casting arm. When in its rest positioning the swing arm will be oriented such that the crucible and the casting mold will be aligned along a line generally tangent with respect to the circle of rotation defined by the adjacent end of the casting arm (the casting mold will be behind the crucible with respect to the direction of rotation of the casting arm, which is always counterclockwise), and as the casting arm is caused to commence rotation, the molten metallic material in the crucible will, as a result of inertial forces, commences flowing into the casting mold. After the casting arm has rotated a short distance (note: its rotational velocity will increase rapidly after commencement of rotation), and after a locking device has been released, the centrifugal forces on the casting mold will cause the swing arm to rotate relative to the end of the casting arm such that the casting mold and the crucible become radially oriented along the line defined by the casting arm. Because the casting mold will be radially outwardly of the crucible, the molten metallic material which has passed into the casting mold will then be centrifugally forced to completely fill the molding space in the casting mold, thus providing a better made product. A centrifugal casting machine of this type is shown, for example, in U.S. Pat. No. 4,130,158.
Although the known crucibles which have been used in conjunction with conventional broken arm-type centrifugal casting machines have been more or less acceptable when used in casting precious metals, they have proven to be insufficient when the casting machines have been used to cast non-precious metals. In this regard, dentists have turned to the use of low gold or non-gold-containing metallic alloys for making their patients' protheses, not only to reduce costs, but to avoid the uncertainties resulting from the daily fluctuations in the prices of the gold and platinum-group metals. However, such non-precious metallic alloys display a lower specific gravity than the conventionally used precious metals, so when they are cast in a broken arm-type centrifugal casting machine, the speed of rotation of the casting arm must be made extremely high so as to provide sufficient inertial and centrifugal forces on the metallic alloys to force them to move out of the supporting crucible and into the casting mold, i.e., so as to fully occupy the molding space in the casting mold. The known crucibles are not fully adequate in this regard, in particular because they do not adequately prevent the non-precious metallic materials therein from splashing out of the crucibles as they are rapidly rotated. Thus results in the unwanted loss of relatively expensive metallic material and/or the production of faulty products.
It is thus an object of the present invention to provide a crucible which can be used to mold non-precious metallic materials in a broken arm-type centrifugal casting machine, i.e., in situations where the casting arms thereof are rotated at extremely high speeds, and which is constructed to prevent loss of the contained molten metallic material due to splashing.